As lightweight and high capacity batteries for use in portable electronic and telecommunication devices and the like such as compact video cameras, cellular phones, and portable personal computers, recently put into practical use are lithium secondary batteries employing a carbon material capable of intercalating and deintercalating lithium ions as the anode active material and a lithium-containing transition metal oxide such as a lithium-containing cobalt oxide (LiCoO2) or a lithium-containing nickel oxide (LiNiO2) as the cathode active material.
However, although lithium-containing transition metal oxides such as lithium-containing cobalt oxide (LiCoO2), lithium-containing nickel oxide (LiNiO2), and the like possess a high battery capacity, they suffered a problem that they have low thermal stability even in a fully charged state due to 50% lithium remaining in the cathode. Moreover, cobalt and nickel, which are the raw materials, are expensive, and their supply is limited. Accordingly, there is proposed a lithium secondary battery using a lithium-containing manganese oxide (LiMn2O4) having spinel type crystal structure as the cathode active material. The lithium-containing manganese oxide (LiMn2O4) is one of the promising materials for use as the cathode active material for a lithium secondary battery, in that manganese used for the raw material is abundant in resources and is inexpensive, and that it yields a high thermal stability in the charged state, such that it can increase the safety of the battery since no lithium is left in the cathode when the battery is fully charged.
U.S. Pat. No. 6,680,143 to Thackeray et al, which is herewith incorporated by reference, discloses the preparation of xLiMO2 (1−X) Li2M1O3 compounds in which M is manganese and M is a tetravalent ion by a hydrothermal process under basic conditions.
U.S. Pat. No. 6,682,850 to Numata et al which is herein incorporated by reference discloses a nonaqueous electrolyte solution secondary battery using lithium-manganese composite oxide for the positive electrode. The lithium-manganese composite oxide is prepared by mixing the Li source and Mn source having a desired particle size at a mole ratio of Li/Mn which matches the lithium-manganese composite oxide and baking in an oxygen atmosphere.
U.S. Pat. No. 6,790,560 to Wakihara et al which is herein incorporated by reference, discloses a positive electrode for a lithium secondary battery which includes a lithium manganese oxide having a spinel structure including a third metal which can be chromium that is prepared by a series of heating at elevated temperatures including heating in air for three days and then calcinating under control oxygen partial pressure.
U.S. Pat. No. 6,818,351 to Sunagawa et al, which is herein incorporated by reference, discloses a positive electrode for a lithium secondary battery using a combination of a lithium containing manganese oxide having a spinel type crystal structure and lithium containing cobalt oxide.
U.S. Pat. No. 6,964,830 to Takahashi, which is herein incorporated by reference, discloses a lithium secondary lithium battery wherein lithium manganate is used as a positive active material represented by LiMn2O4. The manganate is produced by firing a mixture of salt and oxide of the respective elements in an oxidation atmosphere at 650 to 1000° C. for 5 to 50 hours.